How many different kinds of regional variations of pizza exist?

Okay, I'm familiar with NY thin crust versus Chicago deep dish (and the controversies attached to both kinds). But how did the East Coast Sicilian thick crust develop? How is Neopolitan pizza different from thin crust? And how is NJ 'tomato pie' different from NY 'za?
Yes, I know New Haven-famed style 'thin as a whisper' crusted pizza, and California pizza with its weird toppings. But what is Greek pizza, which I hear about in the New England region so often? The entry on St. Louis pizza was really interesting (if alarmingly yellow)--any other oddities?

I was curious if anyone had any answers--and different regional names and oddities they knew of...